Exposure of the public

Public exposure to radiation arises not only from NPPs, but from natural background radiation and artificial sources such as medical diagnostic and therapeutic procedures, nuclear weapons testing, and many occupations that enhance exposure to artificial or natural radiation. All these sources

Activity

(Bq)

Fluence

(cm-2)

deliver doses to members of the public, which are routinely estimated by UNSCEAR.

For as long as they have been on the planet, humans have been exposed to radiation from natural sources, and such exposure has been continually modified by human activities. The main natural sources of exposure are cosmic radiation and natural radionuclides found in the soil and in rocks. Cosmic radiation is significantly higher at the cruising altitudes of jet air­craft than on the Earth’s surface. External exposure rates due to natural radionuclides vary considerably from place to place, and can range up to 100 times the average. An important radionuclide is radon, a gas that is formed during the decay of natural uranium in the soil and that seeps into homes. Exposures due to inhalation of radon by people living and working indoors vary dramatically depending on the local geology, building con­struction and household lifestyles; this mode of exposure accounts for about half of the average human exposure to natural sources. It is now recognized that a very large number of workers are exposed to natural sources in their working places.

Concerns on nuclear test explosions in the atmosphere were the original reason for the UNSCEAR conception. They had been conducted at a number of sites, mostly in the northern hemisphere (the most active testing being in the periods 1952-1958 and 1961-1962), and the radioactive fallout from those tests represents a source of continuing exposure even today, albeit at very low levels. The most dominant peaceful exposure is medical exposure. Irrespective of the level of health care in a country, the medical uses of radiation continue to increase as techniques develop and become more widely disseminated; about 3.6 billion radiological examinations are conducted worldwide every year. (In countries with high levels of health care, exposure from medical uses is on average now equal to about 80% of that from natural sources.)

By contrast, radiation doses due to the generation of electrical energy by NPPs are extremely small in spite of the fact that this type of generation has grown steadily since 1956. Moreover, the doses due to the production of energy in the nuclear reactor are in turn a small part of the doses due to the nuclear fuel cycle, which includes the mining and milling of uranium ore, fuel fabrication, storage or reprocessing of irradiated fuel, and storage and disposal of radioactive wastes. The doses to which the public are exposed vary widely from one type of fuel-cycle installation to another, but in any case they are generally small and they decrease the further the distance from the facility. Moreover, they have been markedly reduced over time because of lower discharge levels. For instance, Fig. 11.2 presents the reduc­tion of normalized noble gas releases for different periods and types of reactor. Over the period 1970-2002, radioactive releases (expressed as 1012 becquerels per 109 watts of electrical energy produced) of noble gases were

FBR LWGR HWR GCR BWR PWR

11.2 Normalized noble gas releases for different periods and types of reactor.

reduced from 13,000 to 112; those for tritium were reduced from 448 to 43, and for iodine from 0.047 to 0.0006 (UNSCEAR, 2011).

In sum, the doses due to the nuclear fuel cycle in general and to NPPs in particular are a tiny fraction of the doses incurred by the population. Table 11.3 presents the latest UNSCEAR estimates of global radiation doses from different sources (UNSCEAR, 2011).